1. Field
Example embodiments relate to methods of manufacturing a semiconductor device. Other example embodiments relate to methods of manufacturing a semiconductor device having a recess channel array transistor (RCAT).
2. Description of the Related Art
As semiconductor memory devices become more highly integrated, memory cells gradually become smaller. As such, a variety of efforts have been made to form a memory device having a desired cell capacitance and/or to increase a cell transistor characteristic in smaller memory cells. As the size of the memory cell decreases, a cell transistor having a smaller size may be needed. To implement a cell transistor having desired characteristics in spite of the miniaturization of the memory cell, a method of controlling the concentration of impurities in a diffusion layer has been researched. As the length of a channel decreases, controlling the depth of the diffusion layer of a transistor becomes increasingly difficult in a variety of thermal treatment processes during a device manufacturing process. As an effective channel length and/or a threshold voltage decrease, a short channel effect occurs. The short channel effect causes problems in the operation of the cell transistor.
To address the above problem, a recess channel array transistor (RCAT), in which a recess is formed on a surface of a substrate and a gate of a transistor is formed in the recess, is being researched. In the RCAT, because the gate is formed in the recess formed in the substrate, the distance between a source and a drain is extended such that the effective channel length increases and the short channel effect decreases.
To manufacture the RCAT, an isolation layer for limiting an active region may be formed on a semiconductor substrate. A recess for forming a gate electrode in the active region of the semiconductor substrate may be formed. An unwanted recess may be form in the isolation layer if the recess is formed in the active region. If a conductive material for a gate is deposited in the recess formed in the active region, the conductive material may also be deposited in the recess that is formed in the isolation layer. As such, if the gate formed in the isolation layer is operated, the gate formed in the recess is affected such that noise is generated. The noise deteriorates refresh characteristics of the gate formed in the active region.